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Crystalline Morphology (crystalline + morphology)

Distribution by Scientific Domains
Polymers and Materials Science100%

Selected Abstracts

Atomic Force Microscopic Observations on the Crystalline Morphology of Poly(ethylene naphthalate)/Clay Nanocomposites

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 16 2007
Yang Choo Chua
Abstract Atomic force microscopic observations on an isothermally crystallized poly(ethylene naphthalate) (PEN)/clay nanocomposite suggest that the presence of nanoclay alters the lamellar organization in PEN mainly in three ways: 1) physically blocking the crystal growth front and creating wide amorphous regions within the spherulites, which may then be filled by secondary lamellae branching out from the primary lamellae of the same spherulite, or primary lamellae developed from other nearby nucleating centers; 2) inducing random twisting of lamellae; and 3) causing irregular crystallite growth fronts, with the protrusion of some leading lamellae. In particular, the physical hindrance imposed by clay tends to be more prevalent for lamellae that grow roughly perpendicular to the clay long axes. This may give rise to an anisotropic crystalline morphology if the clay layers exhibit a preferred orientation induced by flow. [source]

Crystalline morphology and dynamical crystallization of antibacterial ,-polypropylene composite

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008
Xin Chen
Abstract The crystalline morphology and dynamical crystallization of antibacterial polypropylene composite and pure polypropylene were investigated via differential scanning calorimeter (DSC), wide angle X-ray diffraction (WAXD), and real-time hot-stage optical microscopy (OM). The results reveal that the crystalline morphology of antibacterial PP composites changes with variations of the crystallization conditions and compositions. The crystalline phase consists of both ,-PP and ,-PP crystals. The content of ,-PP decreases with the increase in antibacterial agent content and cooling rate. With the addition of ,-nucleating agent, the morphologies of all dynamically crystallized antibacterial PP composites show no obvious spherulitic morphology, and the decrease of crystal perfection and the increase of nucleation density of antibacterial PP composite system could be observed. With the increase of antibacterial agent content, the overall crystallization rates of the antibacterial PP composite increase dramatically, while the content of ,-PP in all antibacterial PP composite decrease distinctly under given cooling conditions. These results can be explained by the interruptive effect of antibacterial agent on interactions of ,-nucleating agent components and the obstructing effect of antibacterial agent on the mobility of PP chains in melts. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Atomic Force Microscopic Observations on the Crystalline Morphology of Poly(ethylene naphthalate)/Clay Nanocomposites

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 16 2007
Yang Choo Chua
Abstract Atomic force microscopic observations on an isothermally crystallized poly(ethylene naphthalate) (PEN)/clay nanocomposite suggest that the presence of nanoclay alters the lamellar organization in PEN mainly in three ways: 1) physically blocking the crystal growth front and creating wide amorphous regions within the spherulites, which may then be filled by secondary lamellae branching out from the primary lamellae of the same spherulite, or primary lamellae developed from other nearby nucleating centers; 2) inducing random twisting of lamellae; and 3) causing irregular crystallite growth fronts, with the protrusion of some leading lamellae. In particular, the physical hindrance imposed by clay tends to be more prevalent for lamellae that grow roughly perpendicular to the clay long axes. This may give rise to an anisotropic crystalline morphology if the clay layers exhibit a preferred orientation induced by flow. [source]

Thermoplastic Polyurethanes with Poly(butylene terephthalate) as Crystallizable Hard Phase

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 3 2008
Debasish De
Abstract Polyurethanes were prepared from poly(tetramethylene oxide) end-capped with MDI and PBT extenders. The PBT extenders were random-disperse in length and their length varied from three to seven repeating units. The structure of the polyurethanes was studied by FT-IR and AFM, their thermal and thermomechanical responses were measured by DSC and DMTA, and their elastic behavior was assessed by compression set measurements. The MDI-PBT-MDI hard segments had a ribbon-like crystalline morphology. Increasing the PBT length gave rise to an increase of the storage modulus at room temperature and the melting point. The storage modulus depended strongly on temperature. [source]

Impact of Nanoscale Confinement on Crystal Orientation of Poly(ethylene oxide)

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 4 2010
Haopeng Wang
Abstract Using a layer-multiplying coextrusion process to fabricate films with thousands of alternating polymer nanolayers, we report here a new crystalline morphology in confined polymer nanolayers and an abrupt transition in the crystallization habit. At higher temperatures, poly(ethylene oxide) crystallizes as large, in-plane lamellae. A 5,°C change in the crystallization temperature produces an on-edge lamellar orientation. The results point to a transition from heterogeneous nucleation to substrate-assisted nucleation. This may be a general phenomenon that accounts for previously unexplained differences in the preferred chain alignment of confined polymer crystals. [source]

Relationship between cell morphology and impact strength of microcellular foamed high-density polyethylene/polypropylene blends

POLYMER ENGINEERING & SCIENCE, Issue 8 2004
Pornchai Rachtanapun
Polymer blends, such as those resulting from recycling postconsumer plastics, often have poor mechanical properties. Microcellular foams have been shown to have the potential to improve properties, and permit higher-value uses of mixed polymer streams. In this study, the effects of microcellular batch processing conditions (foaming time and temperature) and HDPE/PP blend compositions on the cell morphology (the average cell size and cell-population density) and impact strength were studied. Optical microscopy was used to investigate the miscibility and crystalline morphology of the HDPE/PP blends. Pure HDPE and PP did not foam well at any processing conditions. Blending facilitated the formation of microcellular structures in polyolefins because of the poorly bonded interfaces of immiscible HDPE/PP blends, which favored cell nucleation. The experimental results indicated that well-developed microcellular structures are produced in HDPE/PP blends at ratios of 50:50 and 30:70. The cell morphology had a strong relationship with the impact strength of foamed samples. Improvement in impact strength was associated with well-developed microcellular morphology. Polym. Eng. Sci. 44:1551,1560, 2004. © 2004 Society of Plastics Engineers. [source]

Effect of vibration extrusion on the structure and properties of high-density polyethylene pipes

POLYMER INTERNATIONAL, Issue 2 2009
Chen Kaiyuan
Abstract BACKGROUND: The axial strength of a plastic pipe is much higher than its circumferential strength due to the macromolecular orientation during extrusion. In this work, a custom-made electromagnetic dynamic plasticating extruder was adopted to extrude high-density polyethylene (HDPE) pipes. A vibration force field was introduced into the whole plasticating and extrusion process by axial vibration of the screw. The aim of superimposing a vibration force field was to change the crystalline structure of HDPE and improve the molecular orientation in the circumferential direction to obtain high-circumferential-strength pipes. RESULTS: Through vibration extrusion, the circumferential strength of HDPE pipes increased significantly, and biaxial self-reinforcement pipes could be obtained. The maximum increase of bursting pressure and tensile yield strength was 34.2 and 5.3%, respectively. According to differential scanning calorimetry and wide-angle X-ray diffraction measurements, the HDPE pipes prepared by vibration extrusion had higher crystallinity, higher melting temperature, larger crystal sizes and more perfect crystals. CONCLUSION: Vibration extrusion can effectively enhance the mechanical properties of HDPE pipes, especially the circumferential strength. The improvement of mechanical properties of HDPE pipes obtained by vibration extrusion can be attributed to the higher degree of crystallinity and the improvement of the molecular orientation and of the crystalline morphology. Copyright © 2008 Society of Chemical Industry [source]

The effect of crystalline morphology on the degradation of polycaprolactone in a solution of phosphate buffer and lipase

POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 12 2008
M. J. Jenkins
Abstract The degradation of polycaprolactone (PCL) in a solution of lipase and phosphate buffer has been characterized using a combination of differential scanning calorimetry (DSC) and electron microscopy. The molecular weight of the polymer initially appeared to determine the degradation rate while the degree of crystallinity was found to increase with time. Samples of PCL were also conditioned using DSC to specify a known degree of crystallinity. This approach enabled the effects of molecular weight and degree of crystallinity on the degradation to be separated. It was observed that an increase in either molecular weight or degree of crystallinity reduced the rate of degradation. The work presented in this paper addresses a significant limitation associated with the characterization of "as received" samples and provides a more detailed understanding of the effect of polymer morphology on the degradation process. Copyright © 2008 John Wiley & Sons, Ltd. [source]